Patients
We choose three groups of prostate patients (20 patients with volumes ranging from 23 to 76 cc). We included a group of patients with intermediate-risk prostate cancer which are patients with clinical stages T2b to T2c, Gleason score 7, or PSA values 10 to 20 ng/ml. CT simulation is performed for all patients with 3-mm slice thickness under the same protocol (positioned in the supine position). Immobilization was done by the knee and ankle support to ensure fixation and reproducibility; the patient arms are on the chests. We scanned the patient by CT from the abdomen till the mid-thigh to allow contouring all the organs at risk. All patients were immobilized with bladder comfortably full and empty rectum; it is a must in every treatment secession as it is done first before CT scan and setup. The clinical target volume (CTV) included the whole prostate gland and the proximal 1 cm of the seminal vesicles. We created PTV by extending the CTV by 1 cm in all directions except posteriorly (only 6 mm) to decrease dose to the rectum, and also, organs at risk (OARs) (bladder, rectum, and both left and right femoral heads) are outlined. The prescribed dose is (74 Gy/7.5 weeks/37 fractions) with a secession dose limit of 200 cGy/Fr.
Beam arrangement
Varian (TrueBeam) linear accelerator with the Eclipse planning system is used. All beam arrangements were visualized using the beam’s eye view (BEV) display. MLC beam shaping was used to create beam apertures. Asymmetric collimation and other parameters were used when necessary with 3DCRT, IMRT, and RapidArc plans.
We were able to deliver dose to the prostate up to 7400 cGy with 3DCRT plans. The X-ray beam energy used was 6 MV or 15 MV when needed regarding the effective path with tissue density correction. Ten 3DCRT plans used as forward plans for each patient with coplanar beam arrangement techniques were designed. Plan (1) was arranged by angles of 0°, 120°, and 240°: anterior direct with an energy of 6 MV and two lateral (Rt and Lt) oblique wedged (W15) beams with an energy of 15MV. Plan (2) was arrange by angles of 0°, 90°, and 270°, anterior direct and two lateral (Rt and Lt) wedged (W60) beams, all beams with an energy of 15MV. Plan (3) was arranged by angles of 0°, 90°, 180°, and 270°: anterior direct with an energy of 6 MV, posterior direct with an energy of 15 MV, and two lateral (Rt and Lt) oblique beams with an energy of 15 MV, all open without wedges. Plan (4) was arranged by angles of 45°, 315°, 135°, and 225°: two anterior oblique wedged beams (W30 L and W30R are directed with the thin end down and the thick end up) with an energy of 6 MV and two posteriors (Rt and Lt) oblique beams with an energy of 15 MV. Plan (5) was arranged by angles of 0°, 45°, 315°, 135°, 180°, and 225°: all fields are open without wedges and with an energy of 15 MV. Plan (6) was arranged by angles of 0°, 60°, 120°, 240°, and 300°: all fields are open without wedges and with an energy of 15 MV. Plan (7) is a five-field technique and was arranged by angles of 0°, 45°, 90°, 270°, and 315°: all fields are open without wedges and with an energy of 15 MV. Plan (8) was arranged by angles of 0°, 60°, 90°, 120°, 220°, 270°, and 300°: one anterior direct beam, two anterior oblique beams with an energy of 6 MV, two direct lateral (Rt and Lt) wedged (W60L and W60R) beams with an energy of 6 MV, and two posterior (Rt and Lt) oblique beams with an energy of 15 MV. Plan (9) is an eight fields technique (with MLC) were arranged by angles of 0°, 45°, 90°, 135°, 180°, 225°, 270°, and 315°: one anterior direct beam, two anterior oblique beams, two direct lateral (Rt and Lt) wedged (W30 L and W30R are directed with the thin end down and the thick end up) beams, one posterior direct beam, and two posterior (Rt and Lt) oblique, all beams are with an energy of 15 MV. Plan (10) is a plan (9) but without MLC. Plan normalization is set to 100% at beam isocenter, and the PTV is covered by more than 95% isodose; the PTV maximum dose is ranging around 101%. We delivered the dose to the prostate up to 7400 cGy prescription dose by IMRT and RapidArc plans; all beams with an energy of 6 MV. The six-field technique was arranged by angles of 0°, 45°, 90°, 180°, 270°, and 315° with 8 segments per beam (total number of beamlets is 48 openings) and collimator angle of 0°, maximum MU/Fr of 90 MU, and minimum segment area of 1 cm2. The seven-field technique were arranged by angles of 0°, 50°, 90°, 130°, 230°, 270°, and 310° with 6 segments per beam (total number of beamlets is 42 openings) and collimator angle of 0°, maximum MU/Fr of 60 MU, and minimum segment area of 1 cm2. Another seven-field technique was arranged by angles of 0°, 51°, 103°, 155°, 206°, 257°, and 308° with 5 segments per beam (total number of beamlets is 35 openings) and collimator angle of 90°, maximum MU/Fr of 60 MU, and minimum segment area of 1 cm2. While planning, we can increase the penalty weight for both femoral heads until hot spots can reach the acceptable dose limit as hot spots appear near the PTV surface and both femora dose limits may exceed the constraint, taking a long time to achieve optimization. The RapidArc plan was designed with two arcs (179.0° CCW to 181.0° and 181.0° CW to 179.0°) with an energy of 10 MV.